A composition for forming an antireflective film used in a lithography process is known (see Patent Document 1 to Patent Document 4). Patent Document 1 discloses a composition containing a copolymer having a structure unit derived from a benzene nucleus-containing vinyl monomer such as styrene and a structure unit derived from a (meth)acrylamide derivative. The composition is used particularly in a lithography process using an ArF excimer laser as a light source.
Patent Document 2 discloses a composition for forming an antireflective film, containing a copolymer having a structure unit derived from an anthracene nucleus-containing (meth)acrylic acid ester monomer instead of the above structure unit derived from a benzene nucleus-containing vinyl monomer.
Patent Document 3 discloses a composition for forming an antireflective containing a polymer formed using an alkoxyalkyl melamine or an alkoxyalkylbenzoguanamine and having structure units coupled with each other through a crosslinking group bonded to a nitrogen atom, such as —CH2— and —CH2OCH2—.
Patent Document 4 discloses a composition for forming an antireflective film, containing a polymer obtained through a reaction between at least one glycoluril compound and at least one compound containing at least one hydroxyl group and/or an acid.
However, in Patent Document 1 and Patent Document 2, there is no description of a polymer having in the main chain, at least any one of an aromatic ring-containing structure and a nitrogen atom-containing structure. The polymers disclosed in Patent Document 3 and Patent Document 4 are not considered to be a linear polymer.    Patent Document 1: Japanese Patent Application Publication No, JP-A-2000-313779    Patent Document 2 Japanese Patent Application Publication No. JP-A-2001-027810    Patent Document 3: Japanese Translation of PCT International Application No. JP-A-2003-531252    Patent Document 4: International Publication No. WO 2006/030320 pamphlet